My understanding is that the normal way to restore a backup of an entire bootable partition is to boot from the disk or partition on which the backup it resides (which presumably means it's got to be on the local disk or Fireware -- you can't boot over USB, right?). You then use SuperDuper to do the inverse of what you normally do, i.e. copy the backup to the system partition.

Is this possible when the backup is a disk image? Is it possible when the backup is an encrypted disk image?